The present invention relates to a method for evaluating polishing pad surface conditions, a device for the same, and a method for producing thin film devices using the same.
Polishing pads are commonly used in the polishing process of production lines for various electronic parts. A method used in semiconductor device production lines, in which a surface is polished to be plane through chemical and mechanical operations (CMP: Chemical Mechanical Polishing), will be described below as a representative example of a polishing process.
Semiconductor devices are produced by forming devices and wiring patterns on a silicon wafer through deposition, lithography, etching, and the like. In recent years, there has been a growing trend toward miniaturization and multi-layering to provide higher precision and higher densities in devices.
As a result, unevenness of a wafer surface has increased. Such unevenness of a wafer surface makes lithography, which is indispensable for forming wiring patterns and the like, difficult. Thus, planerizing the wafer surface is need. A polishing process method involving CMP is used for this.
An important issue in CMP processing is the management of pad surface conditions used in the polishing process. However, no effective method for performing direct evaluation has been established. Conventionally, pad surface conditions are evaluated indirectly based on changes in polishing rates. The polishing rate is calculated from the polishing amount, generally determined by measuring the film thickness of the item being polished before and after CMP processing, and the processing time in which the actual processing was performed.
An example of this type of conventional technology relating to CMP processing is presented in “Semiconductor planarizing CMP technology” (Doi, Kawanishi, Nakagawa, Kougyouchousakai Ltd.).
CMP processing is generally performed using a processing device shown schematically in FIG. 1. The device includes a polishing pad 1 (hereinafter referred to as pad) and a rotating polishing turntable 2 on which the pad 1 is mounted. A wafer chuck 3 supports the wafer and can move radially over the pad 1 while turning. A conditioner 4 corrects pad deterioration and, like the wafer chuck, moves radially over the pad while spinning. A slurry 5 is used for polishing and is supplied to the pad from a supply nozzle 5a. 
In CMP processing, if a single pad is used to polish a large number of wafers, the pad will deteriorate and the polishing rate will decrease. This reduction of polishing rate results from the fact that the planarity of the pad surface increases as wafers are polished.
This deterioration does not occur uniformly on the pad surface. The deterioration on the pad 1 can form a concentric area 6 as shown in the plan drawing in FIG. 2, spotting 6a as shown in the plan drawing in FIG. 17, or the like. In these figures, areas 7 indicate good areas where there is little deterioration.
In the former case, the concentric area 6 is believed to occur because the pad 1 and the wafer (supported by the wafer chuck 3 but not shown in the figure) in FIG. 1 are both circular. Thus, different degrees of wafer processing take place depending on the radial position on the pad.
In the latter case, the spotting 6a is believed to occur because of bad attachment of the pad 1 to the polishing turntable 2, e.g., air entering during attachment, or localized defects in the pad itself.
In CMP processing, conditioning is performed between processes or during a process in response to pad deterioration. Conditioning refers to cutting the planarized pad surface to increase surface roughness and restore the polishing rate.
One method involves cutting the surface of the pad 1 with a conditioner 4 having a surface on which particles such as diamonds are adhered, thus increasing pad surface roughness.
As the pad surface deteriorates, the uniformity of the wafer surface and processing variations between wafers will be affected. For example, if the concentric area 6 deteriorates as shown in FIG. 2, the wafer center, which is always in contact with the deteriorated area, will have a different polishing rate from the outer area. As a result, the wafer center and the outer perimeter will be processed to different degrees.
In response to problems such as these, there is a need to optimize conditioning conditions by evaluating pad surface conditions. However, the conventional evaluation method is an indirect method that evaluates pad surface conditions from changes in polishing rates calculated from a processing amount calculated from the film thickness before and after polishing and the processing time.
With this type of indirect method, the pad surface conditions cannot be accurately evaluated. Also, evaluation requires time and cannot be performed in response to sudden problems, thus resulting in many defects.
Also, when a single pad has been used for a certain amount of processing, the polishing rate of the pad will not be restored even when conditioning is performed. This condition indicates that the pad has reached its life span and that the pad needs to be replaced. In terms of reducing costs in CMP processing, it would be desirable to maximize the number of wafers processed by a single polishing pad. However, indirect evaluation based on polishing rates will not provide an accurate evaluation of pad surface conditions and there are variations in the polishing rates themselves. Thus, the pad life span cannot be accurately evaluated, resulting in pads being replaced before their life span is reached.